The present invention relates to upgrading a solid material.
The present invention relates particularly, although by no means exclusively, to upgrading solid material which has low thermal conductivity under conditions including elevated pressure and temperature.
The present invention relates more particularly to:
(a) upgrading porous, water-containing, carbonaceous materials (which term includes coal, wood, and biomass) under conditions including elevated pressure and temperature to increase the thermal value of the carbonaceous materials by removing water from the carbonaceous materials; and
(b) cooling the heated carbonaceous materials.
U.S. Pat. No. 5,290,523 to Koppelman discloses a process for upgrading coal by the simultaneous application of pressure and temperature.
Koppelman discloses thermal dewatering of coal by heating coal under conditions including elevated pressure and temperature to cause physical changes in the coal that results in water being removed from the coal by a xe2x80x9csqueezexe2x80x9d reaction.
Koppelman discloses maintaining the pressure sufficiently high during the upgrading process so that the by-product water is produced mainly as a liquid rather than as steam.
Koppelman discloses a range of different apparatus options for carrying out the upgrading process.
In general terms, the options are based on the use of a reactor which includes an inverted conical inlet, a cylindrical body, a conical outlet, and an assembly of vertically or horizontally disposed heat exchange tubes positioned in the body.
In one proposal to use a Koppelman-type reactor, the vertically disposed tubes and the outlet end are packed with coal, and nitrogen is injected to pre-pressurise the tubes and the outlet end. The coal is heated by indirect heat exchange with oil that is supplied as a heat transfer fluid to the cylindrical body externally of the tubes. Further heating of the coal is promoted by direct heat exchange between the coal and steam which acts as a working fluid within the packed bed. In addition, the steam pressurises the tubes and the outlet end to a required pressure.
The combination of elevated pressure and temperature conditions in the tubes and the outlet end evaporates some of the water from the coal and thereafter condenses some of the water as a liquid. A portion of the steam generated following the addition of water also condenses as a liquid in colder regions of the tubes due to the elevated pressure. Steam which is not condensed, and which is in excess of the requirements for optimum pressurisation of the packed bed, must be vented. In addition, non-condensable gases (e.g. CO, CO2) are evolved and need to be vented. Periodically, liquid is drained from the outlet end.
Finally, after a prescribed residence time, the reactor is depressurised and the upgraded coal, with virtually no retained water, is discharged via the outlet end and subsequently cooled.
There are a number of engineering issues and ultimately cost considerations that have inhibited commercialisation of the Koppelman process. There are also spontaneous combustion and dust problems associated with the product.
International applications WO98/30856, WO 98/39613, WO 98/42427, WO 98/50743, WO 98/59209, WO 99/10078 and WO 99/10079 in the name of KFx Inc disclose a series of improvements to the Koppelman process.
U.S. Pat. Nos. 1,679,078, 4,514,912, 4,628,619, 4,502,227, 4,339,306, 4,674,195 and 4,471,536 describe the so-called Fleissner process for upgrading coal.
The Fleissner process was invented in the 1920""s (U.S. Pat. No. 1,679,078) and was developed further in the 1980""s by Voest-Alpine AG (see the other US patents mentioned above). There has been commercial use of the process, mainly in Eastern Europe. The process uses saturated steam to heat batches of coal and removes some water as liquid to avoid a heat of vaporisation penalty. Pressures of 30-60 bar and temperatures of 445-535xc2x0 F. (230-280xc2x0 C.) are used, with a batch cycle time of approximately 160 minutes. Additional flash evaporative drying occurs during depressurisation. Batteries of 4-6 autoclaves are generally required to utilise the waste water and steam energy from each batch reactor. Waste water quality is poor and there are odorous emissions that require scrubbing or incineration. The energy required for upgrading is relatively low. However, spontaneous combustion and dust are problems.
An object of the present invention is to provide an improved method and apparatus for upgrading coal by the simultaneous application of pressure and temperature.
There are two aspects to the present invention.
According to a first aspect of the present invention, in broad terms, there is provided a method for upgrading solid material that includes the steps of:
(a) supplying solid material to a reactor;
(b) heating solid material in the reactor under water saturation pressure conditions and removing water from solid material; and
(c) cooling solid material by depressurising solid material under water saturation conditions.
In more specific terms, the first aspect of the invention provides a method for upgrading solid material that includes the steps of:
(a) supplying solid material to a reactor;
(b) heating solid material in the reactor under water saturation pressure conditions and causing shrinkage of pores of solid material and forcing water from pores as a consequence of pore shrinkage, the water saturation pressure conditions and the heating time being selected so that water is retained in the pores, particularly fine pores, of solid material; and
(c) cooling solid material by depressurising solid material under water saturation conditions and separating water as water vapour from solid material and retaining water in pores, particularly fine pores, of solid material.
The applicant has found that upgraded coal produced by the above-described method of the first aspect of the invention is considerably less likely to spontaneously combust than upgraded coal produced by the above-described known methods and has considerably less dustiness than the known products. In addition, the applicant has found that, unlike the known products, upgraded coal produced by the above-described method can be blended with raw coal without increased risk of spontaneous combustion. Moreover, the applicant has found that both the as-produced upgraded coal and blended product can be stockpiled.
The above-described method of the first aspect of the invention is based to a large extent on the realisation that problems of spontaneous combustion and dust can be significantly alleviated by retaining moisture in pores, particularly fine pores, of solid material.
Heating coal under elevated pressure and temperature conditions causes shrinkage of pores of less than 500 nanometres diameter in coal. Pore shrinkage forces water from pores. The degree of pore shrinkage is highly dependent on coal properties and operating conditions.
In the above-described method of the first aspect of the invention coal is heated under water saturation pressure conditions and is cooled under water saturation conditions. The combination of these heating and cooling conditions and appropriate selection of heating time removes water from pores of coal, and thereby improves the heating value of the coal, but does not remove all the water. The retained water in pores, particularly fine pores, is important because it limits access of oxygen to reactive sites in the pores and thereby reduces the possibility of spontaneous combustion of the coal. In addition, the surface of the product is less hydrophilic than known products and the retained surface water reduces the dustiness of the product.